This invention relates, in general, to a touch detection apparatus and touch control systems for use in conjunction with graphic display device or for controlling a remote device or process.
This invention concerns a touch detection apparatus or touch panel, one use of which is as a selector device for controlling a remotely located device. It is known to use a touch panel in the form of a keypad or keyboard tablet which may be connected to a graphic display or other device and is adapted to be disposed on a desk or work table. Examples of disclosures of such touch control tablets are found in U.S. Pat. No. 3,653,031.
Graphics display devices, of the type herein considered, generally utilize a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display panel (PDP), or any of several other display technologies which in a given application can be used. However, in some applications an actual standard glass window to a real world view could be the desired touch control region.
In the prior are there are three major touch detection systems in common use. The least expensive is an electrically resistive membrane placed in front of a display device. This technique is common in point of sale (POS) applications as typically seen in fast-food restaurants such a McDonalds, Wendy's, etc. The second is infra-red (IR) light beam technology, and the third is acoustic wave technology manufactured for example by ELO and Electro Plasma (licensed under U.S. Pat. No. 4,645,870). This application concerns the third type, utilizing acoustic wave absorbtion technology.
An acoustic touch detection system has a touch sensitive region on which the occurrence and location of a touch is sensed via the touch's effect, typically absorbtion of energy, on the transmission of acoustic waves transversing on or near the surface of the desired touch sensitive region. A common type of acoustic touch control apparatus employs Rayleigh waves, a term which, as used herein, subsumes quasi-Rayleigh waves. Acoustic touch control apparatus employing other types of acoustic waves such as Lamb or shear waves, or combinations of different types acoustic waves, including combinations involving Rayleigh waves, are also known.
Referring now to the drawings, there is illustrated in FIG. 1, the operation of a typical acoustic touch control apparatus having substrate 1 with an active, or touch sensitive region 9, that is defined as being inside the dotted line. A first transmitting transducer 3a is disposed upon the substrate 1 and positioned outside of touch sensitive region 9. The transducer 3a is acoustically coupled to the surface of touch control apparatus substrate 1, and is operable to send an acoustic signal in the form of an acoustic wave 11a traveling parallel to the top edge of touch control apparatus substrate 1 and generally in the plane of touch control substrate 1. Also disposed upon the substrate 1 and aligned in the transmission path of acoustic wave 11a is a linear array of partially acoustically reflective elements 4a, each of which is set an angle to the transmission path and partially reflects, by approximately 90 degrees as shown in FIG. 1, and partially transmits the acoustic signals, creating a plurality of acoustic waves, exemplarily 5a, 5b, and 5c, traveling vertically, or parallel to the Y-axis, across touch sensitive region 9 separated in time. The spacing of reflective elements 4a as shown in FIG. 1 is variable to compensate for the attenuation of the acoustic signals with increasing distance from first transmitter 3a. Acoustic waves 5a, 5b, and 5c, upon reaching the lower edge of touch control substrate 1, are again reflected by approximately 90.degree, as shown by arrow 11b, by another linear array of similarly partially acoustically reflective elements 4b that also are disposed upon substrate 1 towards a first receiving transducer 6a, where the waves are detected and converted to electrical signals for data processing.
Along the left and right edges of touch control apparatus substrate 1 are located a similar arrangement. A second transmitting transducer 3b generates an acoustic wave 12a that propagates along the left edge, with a linear array of partially acoustically reflective elements 4c creating a plurality of acoustic waves, exemplarily 7a, 7b, and 7c, traveling horizontally, or parallel to the X-axis, across touch sensitive region 9. Acoustic waves 7a, 7b, and 7c are redirected, as shown by arrow 12b, by yet another linear array of partially acoustically reflective elements 4d towards a receiving transducer 6b, where the waves are also detected and converted to electrical signals.
If touch sensitive region 9 is touched, for example at position 8, by an object such as a finger or a stylus, some of the energy of the acoustic waves 5b and 7b is absorbed by the touching object. The resulting attenuation is detected by receiving transducers 6a and 6b as a perturbation in the acoustic signal. Analysis of the data with the aid of a microprocessor (not shown) allows determination of the coordinates of position 8, and, if desired, a number relating to the amount of attenuation which may be interpreted as a pressure.
The touch control apparatus substrate 1 may be either a separate plate that is typically made of glass, or another hard substrate material, mounted over a display panel such as a cathode ray tube (CRT), a liquid crystal display (LCD), plasma display panels (PDP), electroluminescent, or other type of display. Alternatively touch control apparatus 1 may be constructed directly on the face of the display panel (e.g., CRT or plasma) itself or onto an optical or EMI filter, whatever is the first contactable surface of the display device.
In normal usage a housing (not shown) typically made of a molded polymer, is associated with touch control apparatus 1. Such a housing usually contains a bezel (not shown) that overlays touch control apparatus 1, cosmetically concealing the transmitting and receiving transducers, the reflective elements, and other components, but exposing touch sensitive region 9. Further, this arrangement protects the concealed components from contamination and/or damage, as well as presenting an aesthetically pleasing appearance, while also defining the touch sensitive region for the user.
The housing bezel may be spaced apart from touch control apparatus substrate 1. In an abutted configuration bezel attenuates the acoustic signals, reducing the touch control apparatus's responsiveness. However, a spaced-apart bezel leaves a gap through which contaminants, such as dirt, dust, and, especially, liquids, may enter and damage or interfere with the function of the concealed components. Acoustic touch control apparatus intended for operation in outdoor environments or in facilities such as restaurants or factories, where exposure to rain, fog, spills, sprays, or cleaning solutions is a likelihood, are especially vulnerable in this regard.
Theoretically, a liquid-impermeable seal can be formed by applying a caulking between the bezel and touch control apparatus substrate 1 around the perimeter of active area 9, but the caulking will absorb acoustic energy, interfering with touch control apparatus operation. Rayleigh wave touch control apparatus, because of the surface-propagating nature of their acoustic waves, are especially likely to be adversely affected. U.S. Pat. No. 5,332,238 to Borucki, hereinafter referred to as the Borucki patent, and incorporated herein by reference, states that a caulking will not only absorb significant amounts of acoustic energy so as to render the touch control apparatus inoperable, but will also acoustically couple the substrate 1 to the screen and can cause a false touch to be registered around the entire perimeter of the screen.
The solution to the sealing problems disclosed in the Borucki patent is to employ a foam strip compressed between the bezel/housing and the touch control apparatus. Acoustic attenuation is limited to an acceptable level by placing an open-cell surface of the foam against the touch control apparatus or by restricting contact with the touch control apparatus to a corner of the foam.
An alternative bezel sealing arrangement is disclosed in U.S. Pat. No. 5,784,054 to Armstrong et al., hereinafter referred to as the Armstrong patent, and incorporated herein by reference, in which a sealing strip made of closed cell foam or, alternatively, expanded polytetrafluoroethylene, is preferably adhesively affixed to the bezel.
Whatever the sealing system, it is operationally desirable to limit acoustic signal loss attributable to the sealant to less than −6 dB as stated in U.S. Pat. No. 6,254,105.
Therefore, while SAW technology has proven to be both ergonomically acceptable and reliable, there are several draw-backs. First, while the printing and firing process applied directly onto a display device provides the best cosmetic arrangement, the process can become rather costly due to the attendant lower manufacturing yields. Second, the placement of the reflector arrays on the display faceplate or glass overlay is associated with significant signal loss due to the attenuation of such surface acoustic waves in glass. This limits the size of touch systems which are in practical use. Furthermore, the reflector arrays, although generally covered with a bezel, are not easily sealed and therefore are exposed to the environment, subject to physical and chemical abuse as well as contamination such a condensing water or spilled drinks such as coffee or soda pop.
Accordingly, it would be desirable to provide an acoustic wave touch control system that could be more easily applied directly to display devices or directly to windows, used over a geometrically larger area, and function under more severe environmental constraints than the prior art systems described above.